Water-hexane interface

Patel S, Brooks CL (2006) Revisiting the hexane-water interface via molecular dynamics simulations using nonadditive alkane-water potentials. J Chem Phys 124(20) 204706... 

Mixed Adsorbed Film of 1-Octadecanol and Dodecylammonium Chloride at the Hexane-Water Interface... 

In the above equations, Y bhe interfacial tension of pure hexane/water interface and Avogadro s number. All the lowest... 

Substituting values from Table 4.1 for the n-hexane-water interface,... 

Simulation. In this study, VSFS and molecular dynamics calculations were employed to examine the structure and dynamics of the hydrogen bonding network of water at the hexane/water, heptane/water and octane/water interfaces in detail [66]. The complementary nature of the approaches has allowed a more detailed understanding of the interface. The calculations provide information not available in the spectroscopic studies, namely the interactions between interfacial water molecules that are isotropically oriented. The direct and iterative comparison of experiment with theory allows for the improvement of the models used to describe water-water and water-solute interactions. 

The results are compared to those above for the CCI4/H2O interface. Several properties of alkane/water and CCU/water interfaces suggest that their interfacial characteristics should be similar. The measured interfacial tensions are 49.7 mN/m for hexane/water and 45 mN/m for CCU/water [73,74], with molecular dipole polarizabilities of 11.9 and 11.2 X 10 cm respectively [75]. However, IR experiments by Conrad and Strauss [76,77] show that water molecules dissolved in an alkane solvent are free to rotate while water dissolved in CCU is relatively constrained. It is the details of these molecular interactions that dominate interfacial structure and dynamics. 

FIGURE 2.12. VSF spectra of the CCLi/water, hexane/water, heptane/water and octane/water interfaces. The solid lines are fits to the data. From Ref. [66]. 

FIGURE 2.14. Calculated (offset) and experimental SF spectra of the CCU/water and hexane/water interfaces. From Ref. [66]. 

Fig. 1. Adsorption isotherms or i-butyric acid at tlie interfaces (l) water-air (2) water-hexane (3) water-benzene (41 water-olive oil. 7 318 K.

Figure 1.32. Non-equilibrium interfacial tension at the oil-water interface system water + hexane, containing palmitic acid, of which the concentration c is indicated. The drawn curves relate to a model interpretation involving diffusion. (Redrawn from J. van Hunsel, G. Bleys and P. Joos, J. Colloid Interface Set 114 (1986) 432.)...

Figure 1.32 deals with adsorption of palmitic acid from hexane to the oil-water interface, using the drop volume method. As the drop volume method is relatively slow, the initial decay from the pristine hexane-water interfacial tension to the first reported data cannot be given. Otherwise stated, the data refer to the later stages of diffusion. The trend is that equilibration is somewhat slower than the adsorption of surfactants from aqueous solution. 

Mukerjee, P. and Handa, T. (1981) Adsorption of fluorocarbon and hydrocarbon surfactants to air-water, hexane-water, and perfluorohexane-water interfaces - Relative affinities and fluorocarbon-hydrocarbon nonideahty effects. Journal of Physical Chemistry, 85(15), 2298-2303. 

Fig. 11 Dynamic interfacial tension (y) measurements of a hexane-water interface during adsorption of nanoparticles to a pendant water drop in hexane (for ail particle types, concentration was 1.2 x 10-4 mmol/L). The gold moieties were modified using dodecanethiol (DDT) or octade-canethiol (ODT). NP homogeneous nanoparticles, JP Janus particles. Reprinted with permission from Langmuir [68], Copyright (2006) American Chemical Society...

A different type of experiments was performed by Van Hunsel Joos (1987b). They studied the steady state of adsorption of various alkanols at the alkane/water interface by means of the drop volume method (Fig. 5.35). The steady states differ remarkably from the equilibrium state. A description of the adsorption process has therefore to allow for a transfer of hexanol molecules across the hexane/water interface. The difference of the two studied steady states is... 

Steady state experiments with hexanol at the hexane/water interface, ( ) - equilibrium values, steady state when hexanol is dissolved in water ( ) and hexane (4), respectively according to Van Hunsel Joos (1987)... 

In experiments on nonionic surfactants, namely Triton X-405 Geeraerts at al. (1993) performed simultaneously dynamic surface tension and potential measurements in order to discuss peculiarities of nonionic surfactants containing oxethylene chains of different lengths as hydrophilic part. Deviations from a diffusion controlled adsorption were explained by dipole relaxations. In recent papers by Fainerman et al. (1994b, c, d) and Fainerman Miller (1994a, b) developed a new model to explain the adsorption kinetics of a series of Triton X molecules with 4 to 40 oxethylene groups. This model assumes two different orientations of the nonionic molecule and explains the observed deviations of the experimental data from a pure diffusion controlled adsorption very well. Measurements in a wide temperature interval and in presence of salts known as structure breaker were performed which supported the new idea of different molecular interfacial orientations. At small concentration and short adsorption times the kinetics can be described by a usual diffusion model. Experiments of Liggieri et al. (1994) on Triton X-100 at the hexane/water interface show the same results. 

In general, interfacial tensions are greater for liquid pairs with low mutual solubilities than for those with high ones. Thus, hexane-water (very low mutual solubility) has an interfacial tension two-thirds that of air-water, whereas butanol-water (reasonably large mutual solubility) has an interfacial tension only a few percent of that of air-water. For miscible liquid pairs such as ethanol-water, there can be no interfacial tension because there can be no interface. 

Fig. 4.20 Vibrational SFG spectra of the neat CCU/water (A), hexane/ water (B) and vapor/water (C) interfaces, indicating the difference in hydrogen bonding at the various interfaces. Reprinted with permission from Ref [56].

Dong, J., Chowdhiy, B. Z. Lehame, S. A. (2003). Surface activity of poloxamines at the interfaces between air-water and hexane-water. Colloid Surface A Physicochem Eng Aspects, 212, 9-17. 

MUK Miiheijee, P., Padhan, S.K., Dash, S., Patel, S., Mohapatra, P.K., and Mishra, B.K., Effect of temperature on pseudotemaiy system Tween-80-butanol-hexane-water, J. Colloid Interface Sci., 355, 157, 2011. 

In addition to the solvent, the system also contained two solutes. These molecules were located in the vicinity of each hexane-water interface. Such an arrangement is computationally more efficient than a system containing one solute molecule at a single water-hexane interface, because information provided from one molecular dynamics trajectory would otherwise require two separate trajectories. 

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